1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, a dry etching method is preformed by the use of a resist mask to form a pattern on a film to be processed, such as an interlayer insulation film film, deposited on a semiconductor substrate. As a degree of integration of semiconductor devices becomes high, patterns become finer and finer. Therefore, a dry etching method should be performed with a high precision in order to delineate finer patterns.
Although a higher degree of integration can reduce a processing area that is processed by a dry etching, a processing depth in the processing area is apt to become deep. In this connection, a ratio of a processing depth to a processing area which is called an aspect ratio tends to become high. Especially, forming a “high-aspect-ratio” pattern is required to obtain a hole pattern which forms lower electrodes of capacitors. However, as an aspect ratio becomes higher, a dry etching method encounters a difficulty in processing.
As a semiconductor device required to have such a high aspect ratio, there is exemplified a DRAM which includes cylindrical capacitors each having a lower electrode, a capacitance insulating film, and an upper electrode. Patent Literature 1 (JP-A 2003-297952) states that a lower electrode of a cylindrical capacitor is more likely to fall down or collapse if the lower electrode becomes thicker or higher. Under the circumstances, Patent Literature 1 has proposed a structure of supporting a lower electrode of each of cylindrical capacitors by a supporter film which is provided on a mold oxide film formed of a BPSG or a silicon nitride film. Specifically, the supporter layer is structured by a line pattern and a frame connected to the line pattern and may be formed by a silicon nitride film. The frame covers a peripheral circuit region formed on a semiconductor substrate (see Claim 1).
Furthermore, according to Patent Literature 1, the line pattern and the mold oxide film are dry-etched so that a conductive region is exposed. A large number of storage node holes are formed in rows and columns. A cylindrical capacitor is formed within each of the storage node holes. Thus, Patent Literature 1 discloses that the supporter film for supporting a lower electrode is formed within each of the storage node holes opened across the line pattern (see Claim 19).
When the cylindrical capacitors are formed by dry-etching a BPSG or a silicon nitride film, as mentioned in Patent Literature 1, deep storage node holes cannot be etched because the silicon nitride film or the like has a low selectivity to dry etching. Therefore, if deep holes for cylindrical capacitors are formed as the storage node holes, problems, such as bowing, may often take place.
Meanwhile, one of reasons why processing becomes difficult about attaining a higher aspect is that a sputtering effect of an ionized etching gas is used to dry-etch a silicon oxide film (SiO2), which has widely been used as a material for an interlayer insulating film. Specifically, when a pattern has deep holes of a higher aspect ratio, ions collide with sidewalls adjacent to each bottom of the pattern. Therefore, the kinetic energy of the ions is attenuated. Thus, the sputtering effect is also lessened. Furthermore, when a silicon oxide film is dry-etched, fluorine radicals are generated from an etching gas including fluorine (F) and bring about isotropic etching. Accordingly, side-etching occurs locally so as to produce a bowing shape. Thus, such side-etching often results in undesired contacts between adjacent pattern portions. It is difficult to avoid those phenomena as long as a silicon oxide film is used in a dry etching process.
Using an amorphous carbon film, which would be hereinafter abbreviated to an AC film, has been proposed instead of a silicon oxide film in order to avoid the above phenomena. A hole having a high aspect ratio can readily be formed by using an AC film because an AC film has a very high selectivity to oxygen-based plasma etching as compared to other films. However, the problem of the AC film is that the AC film cannot be left on a semiconductor substrate. Therefore, the AC film must be removed finally.
Patent Literature 2 (JP-A 2006-135261) has proposed a method of manufacturing cylindrical capacitors using an AC film as an insulating film between sacrifice layers. According to Patent Literature 2, an AC film is dry-etched by using an etching gas primarily containing oxygen (O2). In this method, dry-etching is conducted mainly by radical reactions. Therefore, dry-etching can be advanced irrespective of attenuation of the kinetic energy of ions. Furthermore, since occurrence of bowing due to radical reactions can be suppressed by using an additive gas, a pattern having a high aspect ratio can be formed with high accuracy.
Herein, it is assumed that a supporter layer having a line pattern and a frame connected to the line pattern is used as in Patent Literature 1. In this event, the line pattern of a line shape is connected to the frame and is partially separated and becomes discontinuous due to the formation of storage node holes. Thus, the supporter layer of the line shape has a weak mechanical strength and is insufficient to support the lower layers of a high aspect ratio.
In a case where an AC film is used as a sacrifice layer to support the lower electrodes and is dry-etched as in Patent Literature 2, it has been found out that a further improvement should be required.